The invention relates to a system and method for extracting energy from sea waves with the aid of a buoyancy body, activated by the movement of the sea waves and at least partially immersed in the sea water, and of which the longitudinal extension amounts to a multiple of its height and width and from which cables are run in a splayed-out manner to mutually spaced stationary reference points which are provided beneath the buoyancy body, wherein at least one of the cables is provided as a guide cable for guiding the buoyancy body on a trajectory and at least one cable is provided as a working cable for transmitting the wave energy to at least one energy converter.
In the context of the present invention, an energy converter is understood to mean systems or equipment which are provided to convert the mechanical energy of the buoyancy body into electrical or hydraulic energy using mechanical means.
In order to achieve environmental protection goals, in order to be independent of fossil fuels and to withdraw from nuclear energy, the development of renewable energy sources is being advanced all over the world. A large amount of energy is available in the oceans and seas in the form of sea waves, the potential of which is currently hardly being exploited economically for power generation.
In recent decades, research has been carried out in this area all over the world and many strategies for using sea wave energy have been developed. Thus, a wide range of systems came into being, but only a few of these ever got beyond the prototype stage.
The majority of those projects which led to prototypes ultimately failed during testing owing to the violence of extreme sea motion conditions. In addition, the corrosive conditions of the surroundings presented major problems in relation to the durability of the installations and their functional reliability. Other models remained well behind their predicted system performance in natural sea motion conditions. Only a few of the projects achieved the status of commercial operation, feeding into existing energy supply networks.
The present invention relates to systems in which a relative movement of bodies which are moved vertically, horizontally or in both directions in combination is converted into electrical or hydraulic energy. These so-called systems with moved bodies have received the most attention in the relevant literature since they make it possible to achieve very high degrees of effectiveness, at least from a theoretical point of view.
An evaluation criterion of the systems for wave conversion is the technical degree of effectiveness, i.e., the quotient of installation power and of the available power out of the wave. For a given location and a given installation size it definitively determines the level of the energy yield. Apart from the technical degree of effectiveness, the costs of the system are the major decisive factor for economic operation. These costs are composed of the costs for erecting, maintaining and removing the installation and the costs of the necessary infrastructure. A simple robust construction of a technically efficient installation with a reasonable level of effectiveness which requires high levels of investment and maintenance costs may be considered superior from an overall economic point of view. During the development of new systems for energy conversion from sea waves both criteria must therefore be considered in order to be able to achieve low power production costs.
From the specialist literature (Dr. Ing. Kai-Uwe Graw, “Wellenenergie—eine hydromechanische Analyse”, ISSN 0179-9444, IGAW BUGH Wuppertal, section 8, page 8-8) discloses the operational principle of a floating body which is caused to move with respect to a fixed reference point by waves and in so doing drives an electric generator. For this purpose, the buoyancy body is anchored via a cable system to two spaced-apart fixed points on the sea bed, both in the wave direction and also opposite to the wave direction, in such a way that the cables are splayed at about 45°. One of the anchoring cables is connected as a working cable to two hydraulic cylinders disposed on the buoyancy body, the other is fixed as a guide cable for the buoyancy body both on the buoyancy body and also on the sea bed. Both during upwards and downwards and also during forwards and backwards movements of the buoyancy body as a result of wave motion, the first anchoring cable (working cable) undergoes a relative movement with respect to the body, wherein two hydraulic cylinders are actuated. The hydraulic pressure thus generated is used in an energy converter disposed on the buoyancy body for generator-based power generation.
During this time, the other anchoring cable (guide cable) guides the buoyancy body, in an orientation with respect to the wave which is fixed by the guying directions of the cables, on a trajectory (circular arc segment) about the fixed attachment point.
The French patent application FR 2 869 368 A1 describes a system for energy recovery from sea waves, in which, as in the system described by “Graw”, wave motion both in the horizontal and in the vertical direction can be exploited. For this purpose, a buoyancy body in the form of a disc-like platform is connected with cables which are anchored at one end to three mutually spaced attachment points on the sea bed. From that location, the cables are guided via deflection rollers disposed on the platform to a common ballast body which is disposed centrally below the platform and is attached to the ends of the cables. By reason of its own weight the ballast body always keeps the cables under tension. As the platform moves up and down and to and fro under the influence of the waves, the deflection rollers are driven in alternating directions of rotation by the cables guided thereover and convert the energy by driving an attached generator or a high-pressure pump, which for its part drives a turbine generator unit.
Both systems have disadvantages. The system described by “Graw” has the disadvantage that an efficient trajectory on which the buoyancy body can move can be achieved only when the wave direction corresponds to the orientation of the system. The system cannot adapt to changes in the wave direction, which means that allowances need to be made for loss of performance.
A further disadvantage is seen in that the energy-converting devices and their necessary controls are disposed directly on the buoyancy body where they are directly exposed to the corrosive atmosphere of the sea air and to the sea water. Disruption to operation and failures are therefore to be expected with this described system, in each case a high level of maintenance effort is to be carried out. In addition, the mass of the devices used for energy conversion and control leads to an increase in the overall mass of the moved system, whereby the movement properties are negatively influenced.
The disadvantages described above are partially also to be expected from the system of FR 2 869 368 A1; the energy-converting devices are also disposed directly on the buoyancy body, the platform, in that case. Although the orientation of the buoyancy body with respect to the wave direction is not of significance in this system since the buoyancy body permits the same manner of operation in all directions owing to its disc-like shape, the advantage of the elongate buoyancy body which, when oriented transverse to the direction of wave advancement, is captured by an energy flow of greater width, is thereby sacrificed. A specific trajectory cannot be described with the known system during movement of the buoyancy body since the system does not undergo targeted guidance.
Finally, U.S. Pat. No. 5,066,867 A discloses a system in which the energy-converting devices are disposed in a stationary manner below the sea level which means that disadvantages caused by corrosion and difficult maintenance work are also to be expected in that case. It is also not possible to describe a trajectory during movement of the buoyancy body with this arrangement since the system does not undergo targeted guidance.
Comparable systems are also known from GB 2 015 657 A and from U.S. Pat. No. 5,808,368 A.